The present invention relates generally to the field of semiconductor processing equipment and more specifically to a method and apparatus for eliminating contaminants and residues from inside a vacuum exhaust line connected to a processing chamber and to a method and apparatus for reducing perfluorocompound (PFC) gas emissions from a processing chamber.
During chemical vapor deposition (CVD) processing, deposition gases are released inside a processing chamber to form a thin film layer on the surface of a substrate being processed. Unwanted deposition on areas such as the walls of the processing chamber also occurs during such CVD processes. Because the residence time in the chamber of individual molecules in these deposition gases is relatively short, however, only a small portion of the molecules released into the chamber are consumed in the deposition process and deposited on either the wafer or chamber walls.
The unconsumed gas molecules are pumped out of the chamber along with partially reacted compounds and reaction byproducts through a vacuum line that is commonly referred to as the xe2x80x9cforeline.xe2x80x9d Many of the compounds in this exhausted gas are still in highly reactive states and/or contain residues or particulate matter that can form unwanted deposits in the foreline. Given time, this deposition build-up of powdery residue and/or particulate matter presents a problem. First, the matter is often a pyrophoric substance that may present problems when the vacuum seal is broken and the foreline is exposed to ambient conditions during standard, periodic cleaning operations. Second, if enough of the deposition material builds-up in the foreline, the foreline and/or its associated vacuum pump may clog if it is not appropriately cleaned. Even when periodically cleaned, matter build-up interferes with normal operation of the vacuum pump and can drastically shorten the useful life of the pump. Also, the solid matter may backwash from the foreline into the processing chamber and contaminate processing steps adversely effecting wafer yield.
To avoid these problems, the inside surface of the foreline is regularly cleaned to remove the deposited material. This procedure is performed during a standard chamber clean operation that is employed to remove unwanted deposition material from the chamber walls and similar areas of the processing chamber. Common chamber cleaning techniques include the use of an etching gas, such as fluorine, to remove the deposited material from the chamber walls and other areas. The etching gas is introduced into the chamber and a plasma is formed so that the etching gas reacts with and removes the deposited material from the chamber walls. Such cleaning procedures are commonly performed between deposition steps for every wafer or every N wafers.
Removal of deposition material from chamber walls is relatively straightforward in that the plasma is created within the chamber in an area proximate to the deposited material. Removal of deposition material from the foreline is more difficult because the foreline is downstream from the processing chamber. In a fixed time period, most points within the processing chamber come in contact with more of the etchant fluorine atoms than do points within the foreline. Thus, in a fixed time period, the chamber may be adequately cleaned by the clean process while residue and similar deposits remain in the foreline.
To attempt to adequately clean the foreline, the duration of the clean operation must be increased. Increasing the length of the clean operation, however, is undesirable because it adversely effects wafer throughput. Also, such residue build-up can be cleaned only to the extent that reactants from the clean step are exhausted into the foreline in a state that they may react with the residue in the foreline. In some systems and applications, the lifetime of the exhausted reactants is not sufficient to reach the end or even middle portions of the foreline. In these systems and applications, residue build-up is even more of a concern. Accordingly, there is a need for an apparatus for efficiently and thoroughly cleaning the foreline in a semiconductor processing system and a method of doing the same.
One approach that has been employed to clean the foreline relies on a scrubbing system that uses plasma enhanced CVD techniques to extract reactive components in the exhaust gas as film deposits on electrode surfaces. The scrubbing system is designed to maximize the removal of reactants as a solid film and uses large surface area spiral electrodes. The spiral electrodes are contained within a removable canister that is positioned near the end of the foreline between the blower pump and mechanical pump. After a sufficient amount of solid waste has built up on the electrodes, the canisters may be removed for disposal and replacement.
Problems exist in this prior art method in that the system relies on the large surface area of the electrodes to provide an area for deposited solid matter to collect. To accommodate the large surface area of the electrodes, the system is necessarily large and bulky. Furthermore, extra expenses are incurred in the operation of this prior art scrubber system since the removable canister is a disposable product that must be replaced and properly disposed. Also, the scrubbing system is located downstream from a beginning portion of the vacuum foreline and thus does not ensure removal of powdery material or particulate matter that builds-up in this portion of the line.
From the above it can be seen that an improved method and apparatus for cleaning a foreline is desirable.
Another issue of concern in CVD and other substrate processing apparatus relates to the types of gases and byproducts exhausted from the processing chamber through the foreline. For example, because dissociation of gas within the cleaning plasma is not complete (in some applications only 10% of the introduced gas molecules are dissociated), and the residence time in the chamber of individual molecules in the cleaning gas is relatively short, only a small portion of the molecules released into the chamber react with the deposited material. The gas molecules that do not take part in an etchant reaction are pumped out of the chamber along with the etched away material and reaction byproducts through a vacuum line that is commonly referred to as the xe2x80x9cforeline.xe2x80x9d The exhausted gases are emission byproducts of the semiconductor process.
Many of the fluorine containing gases employed in the semiconductor industry as cleaning etchant gases are referred to as perfluorocompounds or xe2x80x9cPFC""sxe2x80x9d for short. Some of the more commonly used PFC""s include CF4, C2F6, NF3 and SF6 or similar gases. These gases are known to have a long lifetime (up to 50,000 years for CF4), and it is also believed that they have a large global warming potential. Thus, their release into the atmosphere is potentially damaging and is becoming the subject of government and other regulations. Accordingly, it is important to reduce PFC emissions from semiconductor processing equipment such as CVD reaction chambers.
The present invention solves the above problems of the prior art by providing an apparatus that substantially prevents particulate matter and other residual material from building up in an exhaust line of a substrate processing chamber and/or reducing PFC emissions from such a chamber. Different embodiments of the present invention can be specifically designed and optimized for either particle reduction or PFC emissions reduction. It is also possible to design an embodiment optimized for both particle and PFC emissions reduction for use with certain substrate processing operations.
The present invention achieves these goals while being process transparent. That is, in preferred embodiments, operation of the present invention takes no additional processing time to either prevent particulate matter from building up within the foreline or reduce PFC emissions as appropriate. Also, in some preferred embodiments, the present invention does not require the use of additional gases and/or consumable parts.
In one embodiment of the apparatus according to the present invention designed and optimized for particle reduction, a pair of capacitively coupled electrodes define a labyrinthal gas passageway situated between an inlet and outlet of the apparatus. Powder residue and other particulate matter that would otherwise collect in the vacuum line when exhausted from a substrate processing chamber (e.g., during a CVD step) are trapped in the gas passageway. The apparatus can include a plasma generation system that supplies power to the electrodes to form a plasma within the gas passageway. The plasma is formed from unreacted exhaust gases pumped through the gas passageway during a clean cycle. Constituents from the plasma react with the trapped particulate matter to convert the matter into gaseous products that are readily pumped through and out of the exhaust line.
In another embodiment, the apparatus of the present invention includes first and second members having opposing surfaces that define a fluid conduit. The fluid conduit has an inlet, an outlet and a collection chamber between the inlet and the outlet that is structured and arranged to collect particulate matter flowing through the fluid conduit and to inhibit egress of the particulate matter from the collection chamber. A microwave plasma generation system is operatively coupled to the apparatus to form a plasma from etchant gases within said fluid conduit. Constituents from said plasma react with the particulate matter collected in the collection chamber to form gaseous products that may be pumped out of the fluid conduit. In preferred versions of this embodiment of the apparatus, the first and second members are each electrodes and the apparatus also includes a particle trapping system that applies a voltage between the two electrodes to collect particulate matter on the electrode surfaces. The plasma also reacts with this electrically collected matter to convert the matter to gaseous products that may be pumped out of the apparatus.
The gas passageway includes at least one collection chamber that is structured and arranged such that gravitational forces act to collect particulate matter flowing through the passageway and inhibit egress of the particulate matter from the collection chamber. Additionally, a voltage is applied to at least one of the electrodes to create a voltage field between the electrodes that helps collect and trap particulate matter flowing through the passageway.
In other embodiments, the present invention is designed and optimized to reduce PFC emissions from semiconductor processing equipment. One embodiment of such an apparatus includes a vessel chamber that defines a fluid conduit. A source of a PFC oxidizing agent is within the fluid conduit, and a plasma generation system forms a plasma from effluent PFC gases pumped through the apparatus. Constituents from the plasma react with the PFC oxidizing agent to convert the effluent PFC gases to less harmful, water soluble, non-PFC gaseous products and byproducts.
A preferred embodiment of the apparatus of the present invention provides the PFC oxidizing agent within a silicon containing filter. A plasma generation system forms a plasma from effluent PFC gases pumped through the apparatus. Constituents from the plasma react with a silicon containing compound in the filter and convert the effluent PFC gases to less harmful, non-PFC gaseous products and byproducts. In a preferred version of this embodiment, the silicon containing compound is a silicon oxide material.
In another embodiment of the present invention, a gaseous silicon source and/or oxygen source is introduced into the apparatus to provide the PFC oxidizing agent. A plasma is formed from the gaseous silicon source and/or oxygen source and the PFC gas. Constituents from the plasma react to convert the effluent PFC gases to less harmful, non-PFC gaseous products and byproducts.
In still another embodiment of the present invention, a particle trapping and collection system reduces particle build up within an exhaust line connected to a substrate processing chamber and the collected particles and residue provides the PFC oxidizing agent. The particle trapping and collection system traps silicon containing residue from a deposition process that produces such residue. A plasma generation system forms a plasma from the effluent PFC gases. Constituents from the plasma react with the collected residue to convert the effluent PFC gases to less harmful, non-PFC gaseous products and byproducts.
In one version of such an embodiment, a pair of capacitively coupled electrodes define a labyrinthal gas passageway. DC or AC voltage is applied to the electrodes to create a voltage field within the passageway. The voltage field attracts negatively charged particles exhausted through the passageway on one electrode and positively charged particles on the other electrode. The defined passageway also includes at least one area (collection chamber) in which gravitational forces act to trap particulate matter exhausted through the passageway. PFC gases exhausted through the passageway are subjected to RF power applied to the electrodes and excited into a plasma state. Constituents from the plasma react with silicon residue particles trapped in the collection chamber to convert the PFC gases into non-PFC gaseous byproducts.
These and other embodiments of the present invention, as well as its advantages and features are described in more detail in conjunction with the text below and attached figures.